A “stick” electrode is the common vernacular used to describe the type of welding electrode which is used in the SMAW Welding process (shielded metal arc welding).
FIG. 1 illustrates the structure of a conventional stick electrode used in SMAW. As shown there, stick electrode 10 takes the form of a solid, essentially straight, essentially rigid elongated core rod or stick 12 made from a weld filler metal such as mild steel, nickel/steel alloy, chromium/nickel alloy and the like. Core rod 12, which is typically 9 to 18 inches long and 1/16 to ¼ inch in diameter, defines longitudinal surfaces 14, i.e., surfaces running along the length of the rod, which are covered with a coating 16 of weld flux ingredients. Alloying elements for inclusion in the weld metal to be made from stick electrode 10 may also be included in coating 16.
As further shown in FIG. 1, stick electrode 10 defines a distal or “strike” end 18, which is intended to engage the workpiece to be welded and an opposite “holder” end 20, which is intended to be mounted in the holder assembly (not shown) connected to the SMAW welding machine with which stick electrode 10 will be used. For this purpose, a portion of coating 16 is removed from longitudinal surfaces 14 in holder end 20 as shown at 22 in FIG. 1.
After stick electrode 10 has been mounted in place in the holder assembly connected to its welding machine, welding of the workpiece begins by striking an arc (i.e., generating an electrical arc) between the exposed metal tip 19 of strike end 18 of stick electrode 10 and the surface of the workpiece to be welded. In SMAW, this is done by sliding the exposed metal tip 19 strike end 18 along the surface of the workpiece to initiate current flow and then quickly breaking contact between strike end 18 and the workpiece by drawing the two apart slightly. If done properly, electrical current continues to flow between strike end 18 and the workpiece through the small space that separates the two. The intense heat created by this current flow ionizes the surrounding atmospheric gases, thereby generating extremely bright light, i.e., the arc. If strike end 18 is withdrawn from the workpiece too quickly, the arc either will not be generated at all or if generated will extinguish almost immediately. If strike end 18 is withdrawn from the workpiece too slowly, it will melt and thereby bond (i.e., weld) the electrode to the workpiece, referred to as “stubbing out” in the welding industry.
A common problem associated with SMAW welding electrodes of this type is that the exposed metal tip 19 of strike end 18 can carry a significant layer of rust. In manufacture, coating 16 is normally applied to rod 12 in the form of an aqueous flux dispersion, after which the coated rod so formed is heated to evaporate the water of the dispersion and set any binder that may be present. Temperatures as high as 1,000° F. are normally encountered. At these elevated temperatures, and in the presence of the steam generated as a result of evaporating the water of the flux dispersion, exposed metal tip 19 of metal rod 12 readily oxidizes since it is not covered with any type of protective layer. As a result, a layer of rust normally forms on this tip. Unfortunately, this layer of rust can prevent stick electrode 10 from operating properly, since it not only prevents intimate physical contact between the workpiece being welded and exposed metal tip 19 of strike end 18 of electrode 10 but also because of its poor electrical conductivity.
To deal with this problem, it has already been proposed to apply electrically conductive protective coating 24 to exposed metal tip 19 of strike end 18 of electrode 10 during its manufacture. For this purpose, an aqueous dispersion of particulate graphite and an inorganic binder is normally applied to this exposed metal tip after the aqueous flux dispersion forming coating 16 is applied but before the coated rod so formed is fired. When the modified rod so formed is then fired, the water in this graphite dispersion evaporates and the inorganic binder in the dispersion fuses to form a coherent binder holding the individual graphite particles in place on exposed metal tip 19 of strike end 18. Waterglass (sodium silicate) is normally used as the inorganic binder, not only because it can withstand the high temperatures involved during firing but also because it can prevent oxidation of exposed metal tip 19 of strike end 18 during the firing process. Meanwhile, graphite particles are used to provide electrical conductivity to protective coating 22, not only because of their high electrical conductivity but also because they readily decompose to form a benign by-product, CO2, as soon as welding begins.